Solid state drives (SSDs) are becoming a popular alternative to conventional hard disk drives. SSDs differ from conventional hard disk drives in several ways. For example, SSDs have semiconductor properties, have no moving parts, and have inherent parallelism.
Even though SSDs have the potential to replace hard disk drives, a major barrier to the adoption of SSDs is their limited lifetime. SSDs are built using NAND flash memory, which limits the number of write operations that can be issued to a flash memory block. A memory block must be erased before each overwrite and such erasures decrease the lifetime of the SSD. Additionally, as the cost of NAND flash memory has declined with increased bit density, the number of erase cycles (and hence write operations) that a flash memory can tolerate has suffered.
Moreover, general purpose operating system workloads are hard on the storage subsystem, particularly in terms of write volume and non-sequentiality. The combination of a more stressful workload and fewer available erase cycles reduces useful lifetime of SSDs, in some cases to less than one year.